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Duct Airflow and Sensible Heat
Estimate airflow through a rectangular duct and the dry air's sensible heat change using specified average velocity, density and constant-pressure heat capacity.
Input parameters
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Results
Duct area: m²
Volume flow: m³/s · m³/h
Mass flow: kg/s
Positive means the outlet temperature is higher; negative means it is lower. Volume flow refers to the duct measurement state. The heat-transfer interpretation requires the conditions below.
Equations
A = width × height
V̇ = A × v
ṁ = ρ × V̇
ΔḢT = ṁ × cp × (Tout − Tin)
Use metres, m/s, kg/m³ and J/(kg·K); Celsius differences equal kelvin differences.
Applicability
- Steady flow, rectangular clear internal dimensions and cross-section averaged velocity.
- Dry air at constant mass flow, with negligible pressure effects on enthalpy; density must match the velocity measurement section and the specified average constant-pressure heat capacity must represent the temperature range.
- When shaft work and kinetic and potential energy changes are negligible and no other mass crosses the boundary, the enthalpy-rate change approximates net heat transfer to the air. When finding equipment heating or cooling duty, include significant fan work and external heat losses in a complete energy balance.
- Humidity, condensation, latent load, leakage and actual velocity profiles are not calculated. Width and height are converted when the dimension unit changes.
Worked example
0.5 m × 0.3 m at 2 m/s gives 0.3 m³/s. With ρ = 1.2 kg/m³, cp = 1006 J/(kg·K) and heating from 20 to 30 °C, the estimated temperature-related enthalpy-rate change is +3621.6 W; under the conditions above it approximates net heat transfer.
Default density and constant-pressure heat capacity are illustrative. Replace them with values appropriate to the measurement and temperature range.
Engineering estimate only; verify actual conditions and applicable design requirements.